Back to EveryPatent.com
| United States Patent |
5,281,682
|
|
Cornforth
, et al.
|
January 25, 1994
|
Radiation curable compositions and method of use
Abstract
Improved radiation curable compositions are provided which comprises
N-vinylformamide and an oligomer selected from the group consisting of
epoxy-acrylate resins, polyester acrylate resins, polyurethane acrylate
resins and mixtures thereof. A photoinitiator is also added to the
composition. A process is also provided whereby the composition is applied
to the surface of a substrate and subsequently exposed to a radiation
source until an adherent dry polymerized film is formed on the substrate.
These compositions are useful as pigmented and unpigmented coatings,
printing inks, adhesives and the like.
| Inventors:
|
Cornforth; David A. (Rochdale, GB2);
Fowler; Dawn (Water Rossendale, GB2);
Renz; Walter L. (Macungie, PA)
|
| Assignee:
|
Air Products and Chemicals, Inc. (Allentown, PA)
|
| Appl. No.:
|
845284 |
| Filed:
|
March 3, 1992 |
| Current U.S. Class: |
526/273; 525/920; 526/307.2; 526/328.5; 528/271 |
| Intern'l Class: |
C08F 224/00; C08F 226/02; C08F 220/10; C08G 071/04; C08G 063/00 |
| Field of Search: |
525/296
526/273
|
References Cited
U.S. Patent Documents
| 3874906 | Apr., 1975 | Prucnal et al. | 117/93.
|
| 4129709 | Dec., 1978 | Lorenz et al. | 526/264.
|
| 4348427 | Sep., 1982 | Priola et al. | 427/44.
|
| 5106875 | Apr., 1992 | Horn et al. | 521/137.
|
Primary Examiner: Schofer; Joseph L.
Assistant Examiner: Cheng; Wu C.
Attorney, Agent or Firm: Rodgers; Mark L., Marsh; William F., Simmons; James C.
Claims
We claim:
1. A radiation curable formulation comprising:
(a) an oligomer selected from the group consisting of epoxy-acrylate
resins, polyester acrylate resins, polyurethane acrylate resins and
mixtures thereof; and
(b) N-vinylformamide.
2. The formulation of claim 1 which also contains a mono-, di, or
polyfunctional vinyl or acrylic monomer.
3. The formulation of claim 1 wherein N-vinylformamide is present in the
formulation from about 2 to 40 wt % of the total formulation.
4. The formulation of claim I wherein said oligomer is a polyurethane
acrylate resin.
5. The formulation of claim 4 wherein said polyurethane acrylate is
di-functional.
6. The formulation of claim 1 which has a viscosity of between about 32.5
and 10.0 poise.
7. The formulation of claim 1 which also contains a photoinitiator.
8. The formulation of claim 1 wherein N-vinylformamide is present in the
formulation from about 5 to 25 wt % of the total formulation.
Description
FIELD OF THE INVENTION
The present invention relates to the formulation and applications of
radiation curable compositions suitable for use as pigmented or
unpigmented coatings, printing inks, adhesives and other applications.
BACKGROUND OF THE INVENTION
Radiation curable acrylic oligomers are usually comparatively high
viscosity species and require to be blended with a monomer in order to
produce a radiation curable formulation of the appropriate viscosity for
any particular application. Such oligomers generally fall into three broad
groups of resin, namely epoxy-acrylates, polyester acrylates and
polyurethane acrylates.
The epoxy-acrylates include the B-hydroxy esters which are generated by the
reaction of acrylic acid or methacrylic acid with an epoxy resin or
epoxy-novolak resin. The polyester acrylates consist of polyesters which
have been esterified with acrylic acid to yield a polyester with acrylate
ester terminal groups, using well established esterification techniques.
The polyurethane acrylates consist of reaction products of a
hydroxy-containing acrylate ester, usually 2-hydroxyethyl acrylate or
hydroxy propyl acrylate with an isocyanate prepolymer.
The monomers which are blended with the above acrylic oligomers in order to
yield a practical radiation curable formulation in the presence of a
suitable photoinitiator fall into three groups defined by functionality,
and may be mono-, di- or poly-functional.
Poly-functional monomers,- usually with a functionality of 3 or 4,
generally consists of acrylate esters of tri or tetra-functional alcohols.
Commonly used materials include glycerol triacrylate, trimethylol propane
triacrylate, trimethylol ethane triacrylate, pentaerythritol tetracrylate,
together with the acrylates of the ethoxylates or propoxylates of the
above alcohols.
Di-functional monomers consist usually of the acrylate esters of ethylene
glycol or propylene glycol and their oligomers, with tripropylene glycol
diacrylate being especially preferred, diacrylates of longer chain
alcohols such as hexanediol diacrylate and acrylate esters of
cycloaliphatic diols such as the cyclohexane diols.
Mono functional monomers consist of the acrylate esters of mono functional
alcohols such as octanol, nonanol, decanol, dodecanol, tri decanol and
hexadecanol both in their linear and branch chain forms. Also included are
cyclohexyl acrylate and its alkyl derivatives such as t-butyl cyclohexyl
acrylate, tetrahydro furfuryl acrylate. N-vinylpyrrolidone has also been
used as a mono-functional monomer. Styrene is used in certain formulations
but is not widely used in this technology due to triplet quenching.
High functionality monomers give rapid cure speeds and high cross-link
density, leading to films of high hardness and tensile strength with
excellent chemical resistance. The films however suffer from reduced
adhesion. Such monomers exhibit comparatively poor ability to reduce the
working viscosity of the oligomer, due to the higher initial viscosity
associated with the monomers themselves. Mono functional monomers,
conversely, give slow cure speeds and low cross-link density, leading to
cured films of lower hardness, tensile strength, and with reduced chemical
resistance. Such monomers give films with improved elongation and improved
adhesion, and the monomers show a considerably increased capacity to
reduce the working viscosity of the oligomer.
Prucnal, et al., U.S. Pat. No. 3,874,906 teach a method of applying and
curing a polyester-acrylate containing coating composition comprising
adding N-vinylpyrrolidone to the composition and subsequently applying the
composition to a substrate and subjecting it to actinic light to cure.
Lorenz, et al., U.S. Pat. No. 4,129,709 disclose a coating composition
comprising an oligomer produced by reacting polytetrahydrofuran with a
diisocyanate, N-vinyl-2-pyrrolidone and an acrylic acid ester having a
boiling point of at least 200.degree. C. at 760mm Hg.
Pviola, et al., U.S. Pat. No. 4,348,427 teach a method of coating surfaces
by applying to the surface to be coated, a mixture composed by at least
one compound such as an epoxy-acrylate resin, a polyester
alpha-omega-acrylate resin, an unsaturated polyester resin, or a
urethane-acrylate resin and by at least one unsaturated compound of the
amide, lactam, piperidone and urea classes and subsequently irradiating
the coated surface with radiation in the range of 200 to 400mm.
SUMMARY OF THE INVENTION
The present invention is an improved radiation curable composition
comprising an oligomer selected from the group consisting of
epoxy-acrylate resins, polyester acrylate resins, polyurethane acrylate
resins and mixtures thereof, and N-vinylformamide. A photoinitiator is
added to the composition prior to applying the composition to a substrate.
Optionally, the composition may contain other reactive monomers such as
mono-, di-, or poly-functional acrylic esters, or other vinyl compounds.
The present invention also covers a process for coating a substrate
surface using the subject composition. In accordance with this process,
the composition containing the photoinitiator is applied to the substrate
surface and is subsequently exposed to a radiation source until an
adherent dry polymerized film is formed on the substrate.
We have discovered that the use of N-vinylformamide as a monomer radiation
curable coating formulations results in a superior coating material
compared to prior art formulations. Compared to acrylate types of
monomers, N-vinylformamide exhibits superior capacity to reduce the
working viscosity of the oligomer, and is especially useful with
polyurethane acrylate containing formulations with which viscosity
reduction is particularly difficult with monomers traditionally used with
such systems. Additionally, films cured with N-vinylformamide demonstrate
excellent hardness, chemical resistance, flexibility, scuff resistance and
scratch resistance.
DETAILED DESCRIPTION OF THE INVENTION
We have discovered improved radiation curable compositions which are useful
for forming a hard protective polymer films on substrate surfaces. The
composition is an improvement over the prior art in that when
N-vinylformamide (NVF) monomer is blended with an acrylic oligomer system,
the resultant formulation exhibits improved properties for applications
such as protective and decorative coatings, resinous binders for pigmented
inks, adhesive materials and the like. We have found that NVF is an
effective reactive diluent for radiation curable oligomer systems in that
it exhibits low vapor pressure, good solvency, and rapid cure under
standard photocure conditions to hard, flexible, clear, colorless
coatings. Additionally, NVF significantly reduces working viscosities
relative to traditionally used acrylate monomers, particularly in
difficultly reducible polyurethane acrylate oligomer systems. Cured
polymers made with NVF exhibit improved odor, harder films, good chemical
resistance, flexibility, scuff resistance and scratch resistance.
A further advantage of using NVF is that, since NVF is a secondary amide,
the amide hydrogen is available as a reactive site for secondary curing
reactions. Consequently, under proper conditions, the NVF will combine
with species normally reactive with active hydrogen compounds to produce a
separate non-volatile induced cure subsequent to or concurrent with free
radical polymerization through the vinyl bond. Such secondary curing
reactions are characteristic of so-called dual cure systems, and can be
useful in modifying the finished properties of the film.
The formulation is made by mixing NVF with an appropriate acrylate resin.
The NVF is typically added in a concentration of between about 2 and 40 wt
% and preferably between 5 and 25 wt % based on the total composition. The
acrylate resins useful for such compositions include epoxy-acrylates,
polyester acrylates and polyurethane acrylates. Optionally, the
composition may contain other reactive species such as the aforementioned
acrylic monomers consisting of mono-, di-, or polyfunctional acrylic
esters of suitable low molecular weight alcohols, acrylic esters of
ethoxylated or propoxylated alcohols, diols, and triols; or other vinyl
monomers.
"Epoxy-acrylates" are the B-hydroxy esters which are generated by the
reaction of acrylic acid or methacrylic acid with an epoxy resin. Suitable
epoxy resins are the resinous products generated by reaction of
Bisphenol-A or Bisphenol-F with epichlorohydrin, and consist of a range of
materials including liquid and solid resins of varying molecular weights.
Especially preferred are the liquid Bisphenol A - epichlorohydrin
condensates with a molecular weight in the range of from 300 - 600. The
description "epoxy-acrylate" may also be applied to reaction products of
acrylic acid or methacrylic acid with epoxy-novolak resins, that is resin
obtained by reaction of epichlorohydrin with a phenol or cresol
formaldehyde condensate, and which contain a plurality of glycidyl ether
groupings with an epoxy functionality greater than 2. Also included are
the comparatively low viscosity epoxy acrylates obtained by reaction of
epichlorohydrin with the diglycidyl ether of an aliphatic diol or polyol.
Examples of materials which may be reacted with acrylic or methacrylic
acid include hexanediol diglycidyl ether, neopentyl glycol diglycidyl
ether and butanediol diglycidyl ether.
The polyester acrylates consists of polyesters as defined and described in
the above description which have been esterified with acrylic acid to
yield a polyester with acrylate ester terminal groups, using well
established esterification techniques.
Polyurethane acrylates consist of reaction products of a hydroxyl
containing acrylate ester, usually 2-hydroxyethyl acrylate or hydroxy
propyl acrylate (1-methyl, 2-hydroxyethyl acrylate) with an isocyanate
prepolymer. Such a prepolymer consists of the reaction products of a
polyol, which may be a polyether polyol or a polyester polyol, with a di
or polyisocyanate. Suitable polyether polyol include for example
polyethylene glycols, polypropylene glycols, ethoxylated or propoxylated
glycerol or ethoxylated or propoxylated glycerol or ethoxylated or
propoxylated trimethylol propane or trimethylol ethane, all of which may
have molecular weights in the range of about 1000 to about 6000. Suitable
di or polyisocyanates include the aromatic isocyanates such as toluylene
di-isocyanate or di phenyl methane di-isocyanate, the araliphatic
diisocyanates such as tetramethyl xylylene di-isocyanate, and aliphatic or
cycloaliphatic di-isocyanates such as isophorone-di-isocyanate,
bis-isocyanate cyclohexyl methane, hexamethylene di-isocyanates and alkyl
substituted hexamethylene di-isocyanates.
Suitable polyester polyols, which may be reacted with the above range of di
or poly isocyanates, include hydroxy terminal polyesters obtained from a
wide range of di and poly functional carboxylic acids and a wide range of
di and poly functional alcohols. Suitable acids include adipic, sebacic,
glutaric and azelaic acids, the isomeric phthalic acids, trimellitic acid
and pyromellitic acid. Suitable polyols include for example ethylene and
propylene glycols and their oligomers, cyclohexane diols and their
ethoxylates and propoxylates, and higher functionality polyols such as
glycerol, trimethylol propane and trimethylol ethane and their ethoxylates
and propoxylates. Also included are poly-caprolactone polyols.
The resultant acrylate oligomer/NVF compositions are mixed with a
conventional photoinitiator used in this technology, which include for
example, benzophenone, benzoin ethers and related species, as well as
cationic photoinitiators. Monomers including t-amino groups may be used in
certain formulations as activators for the photoinitiator.
The composition, containing the photoinitiator, is applied to the surface
of a substrate and subsequently exposed to a radiation source until an
adherent dry polymerized film is formed on the substrate. The composition
is useful for placement on a wide range of substrates including paper,
rigid and flexible plastics, metallic substrates, cement, glass, asbestos
products, wood and the like.
The following examples are presented to better illustrate the present
invention and are not meant to be limiting.
EXAMPLE 1
This example demonstrated the effect of increasing the proportion of a
mono-functional monomer in a formulation consisting of a blend of
Actocryl-305 which is a commercially available polyurethane acrylate of
functionality 2. "Actocryl" is a registered trademark of Anchor Chemical
Group plc. This data demonstrates the superior viscosity reducing power of
N-Vinylformamide when compared to a typical mono-acrylate, i.e., isodecyl
acrylate, and also the greater range of compatibility of N-Vinylformamide
compared to the mono-acrylate. The viscosities for various formulations
using isodecyl acrylate and those using NVF are reported in Tables 1 and
2, respectively. The formulations are in wt % of each component based upon
total weight of the formulation.
TABLE 1
______________________________________
FORMULATION:
A B C D E F
______________________________________
Actocryl-305
60 60 60 60 60 60
Tripropylene
35 30 25 20 15 10
Glycol Diacrylate
Isodecyl Acrylate
5 10 15 20 25 30
Viscosity, 33.3 25.7 21.7 18.5 21.0*
Incompat-
(poise 25.degree. C.) ible
______________________________________
*Cloudy
TABLE 2
______________________________________
FORMULATION:
G H I J K L
______________________________________
Actocryl-305
60 60 60 60 60 60
Tripropylene
35 30 25 20 15 10
Glycol Diacrylate
N-VinylFormamide
5 10 15 20 25 30
Viscosity, 32.5 24.0 19.5 14.0 12.5 10.0
(poise 25.degree. C.)
______________________________________
The results reported in the above tables clearly show that NVF has a
significantly greater ability to reduce the viscosity of such a
formulation, and also exhibits better compatibility at higher
concentrations than the mono-acrylate.
EXAMPLE 2
Formulations B and H from Example 1 were compared for chemical resistance
as follows: 100 pts of each formulation were compounded with 3 pts of
Irgacure-184 photoinitiator ("Irgacure" is a trade name of Ciba-Geigy). 6
micron varnish films of each formulation were drawn down on aluminum
panels and radiation cured at 400 f.p.m. using a 200 watt/in medium
pressure lamp.
The chemical resistance of the resultant films was determined by the
standard MEK double rub test. The results of this test are set out in
Table 3 below:
TABLE 3
______________________________________
MEK DOUBLE RUBS
No. of passes
FORMULATION B + FORMULATION H +
at 400 f.p.m.
3 phr IRAGURCE 184
3 phr IRGACURE 184
______________________________________
4 12 14
6 10 18
8 10 34
10 10 (Tacky) 28
______________________________________
The results of Table 3 above show that Formulation H (containing NVF)
exhibited superior chemical resistance over Formulation B.
EXAMPLE 3
Since the acrylate ester did not produce a hard film, the hardness of
N-Vinylformamide films (formulation H) were assessed against a formulation
containing N-Vinylpyrrolidone monomer as taught in the prior art. The
formulation containing the N-Vinylpyrrolidone had the composition as set
out as Formulation "M" in Table 4.
TABLE 4
______________________________________
FORMULATION*: H M
______________________________________
Actocryl-305 60 60
Tripropylene Glycol Diacrylate
30 30
N-Vinylformamide 10 --
N-Vinylpyrrolidone -- 10
Irgacure 184 3 3
______________________________________
*all reported as wt % based upon the total weight of the formulation.
24 micron films of Formulations H and M were cast on separate aluminum
panels, and hardness was assessed after varying numbers of passes at 400
feet per minute (f.p.m.) radiation exposure using the pendulum hardness
technique. The results of this test are set out in Table 5 below.
TABLE 5
______________________________________
Curing
Passes at 400
FORMULATION H FORMULATION M
f.p.m. NO. OF PENDULUM SWINGS
______________________________________
4 39 24
5 42 32
6 38 40
8 37 30
10 44 38
15 52 40
______________________________________
The results reported in Table 5 above show that the films made from
Formulation H typically exhibited greater hardness than the formulation
using N-vinylpyrrolidone which was commonly used for prior art coating
applications.
Having thus described the present invention, what is now deemed appropriate
for Letters Patent is set out in the following claims.
Top